1. Field of the Invention
The present invention relates to an output device for outputting a recorded product having an image corresponding to an electronic document formed thereon from the electronic document, an image processing device and method for generating an image signal which can be output to a display device, an image processing system and output device which employ the image processing device or image processing method, and a recording medium which can be read by a computer storing a program for causing the computer to execute these processing operations.
2. Description of the Related Art
In a DTP (Desktop Publishing) system, an image is generally formed and edited on a display device such as a CRT (Cathode Ray Tube) and a final document is output from an output device as a hard copy. Various devices have been developed as the display device and output device used, and not only one device but multiple devices are now in use. This device environment has such a problem that even when the same color image is to be output, colors vary according to the characteristic properties of a display device and an output device in use.
To control colors output from each device uniformly, CMS (Color Management System) has been introduced. Particularly, profile type color management established by ICC (International Color Consortium) has become standards in fact.
FIG. 28 is a diagram showing an example of conventional color management method proposed by ICC. In FIG. 28, reference numeral 101 denotes an electronic document, 102 color appearance model conversion unit, 103 device color correction unit, 104 to 107 display devices, 108 output conversion unit, 109 output device, 110 to 112 light sources, and 113 a recorded product. In the system, color management is carried out by converting into device independent color space. The device independent color space at this point is CIE1931XYZ chromaticity or CIE1976L*a*b* uniform color space.
As shown in FIG. 28, to display the electronic document 101 on the display devices 104 to 107, the color appearance model conversion unit 102 changes the color temperature of the electronic document 101 to a color temperature set or estimated by the display devices 104 to 107. As the color appearance model, for example, models proposed by von Kries, Hunt, Nayatani, Fairchild, Luo and the like are famous but CIECAM97s which makes use of the characteristic features of these models has recently been proposed.
Further, the device color correction unit 103 converts an image signal whose color temperature has been changed to a color temperature set or estimated by the display devices 104 to 107 by means of the color appearance model conversion unit 102 into color spaces specific to the display devices 104 to 107 using color conversion coefficients stored in a profile specified by ICC.
For instance, when a display device is of a general type which does not enable a user to control its color temperature, it generally has a color temperature of around 9300 K like the display device 107. The estimated color temperature of the electronic document 101 is D50 or D65 which is the color temperature of an ordinary light source in most cases. If the electronic document has a color temperature of D50, the color temperature of the electronic document 101 is changed from D50 to 9300 K by the color appearance conversion unit 102. Thereafter, the device color correction unit 103 converts the color temperature into color space specific to the display device 107 to be displayed on the display device 107.
The output device 109 forms an image on a recording medium to generate a recorded product on the assumption of D50 illumination in most cases. When the color temperature of the electronic document 101 is D50, it is converted into color space specific to the output device 109 by the output conversion unit 108. When the color temperature of the electronic document 101 is D65, the color appearance model conversion unit is provided to change it to D50 which is then converted into color space specific to the output device 109. Thus, the recorded product 113 having an image formed by the output device 109 is referred to by a user under light sources 10 to 112 having respective color temperatures. That is, the same recorded product 113 is referred to under the light sources 110 to 112.
This color management method has two big problems. One is that the colors of images output from respective devices completely differ from one another because the color temperature of each image depends on a color temperature set by a device such as any one of the display devices 104 to 107 or the output device 109. For example, when an image edited on the display device 107 which emits light at 9300 K is output to the output device 109 based on the assumption of D50 illumination to form an image and the image is compared with the image on the display device 107 under the light source 111 of D50, they look completely different in color. When the electronic document 101 is observed on the other display devices 104 to 106, the original color of the electronic document 101 may not be seen because the color temperature of the color document 101 depends on a color temperature set by each display device. These are inconvenient for users to form and edit an image. However, at an actual working site, these are considered as natural and left as they are.
The other problem is that the influence of environmental light is not taken into full consideration. For example, consider a case where an image formed on a recorded product and an image displayed on a display device are compared with each other at the same time under a light source having a color temperature of about 4000 K. In ICC's conventional method, the color temperature of the display device is set to 4000 K, the color appearance model conversion unit 102 is used to change the color temperature, the device color correction unit 103 converts device independent color space into color space specific to the display device using a color conversion coefficient corresponding to a color temperature of 4000 K, and the image is output.
The color appearance model can estimate color corresponding to a changed environment by grasping changes in the visual characteristics of a human being caused by a change in the color temperature of environmental light. However, it cannot estimate a color change caused by changes in the characteristic properties of a light source for observing a recorded product. For example, when a recorded product output on the assumption that it is observed under D50 illumination is observed under a light source having a color temperature of about 4000 K, a color difference is produced by changes in the characteristic properties of a light source. Particularly, in the case of xerography, this tendency is more conspicuous than photography. The color difference cannot be estimated with a color appearance model. This problem does not arise when the recorded product is observed under a specified light source. However, in an actual environment that a general user uses a DTP system, the observation light source is a fluorescent lamp (around 4000 K) which is generally used at offices in most cases although the output device has a set color temperature of D50. As described above, the color difference problem caused by changes in the characteristic properties of a light source cannot be solved by the conventional method.
Thus, the original appearance of the electronic document cannot be easily output from the display device and output device by the current color management method in most cases. When a recorded product is simulated on a display device, a simulation image does not agree with an image on the recorded product in terms of the appearance of color. Therefore, a user must adjust color to achieve his intended color, taking great time and labor to adjust color.
The present invention has been made in view of the above circumstances and provides an image processing device and image processing method which reproduce the original color of an electronic document faithfully on an output device for generating a recorded product having an image formed thereon or a display device for displaying an image, can simulate the appearance of color of a recorded product on a display device accurately and can simulate a second recorded product with a first recorded product. The present invention also provides an image processing system and an output device incorporating the image processing device or method and a recording medium which can be read by a computer storing a program for causing the computer to execute these processing operations.